The Swiss Competition Commission said it’s investigating UBS AG, Credit Suisse Group AG and six more banks as the probe into the alleged manipulation of foreign-exchange rates deepens.

The authorities are examining whether firms colluded to fix foreign-exchange rates, the Bern-based watchdog, also known as Weko, said in a statement today. JPMorgan Chase & Co., Citigroup Inc., Barclays Plc and Royal Bank of Scotland Group Plc are among the other firms being probed, along with Zuercher Kantonalbank and Julius Baer Group Ltd., Weko said. More banks and brokers may have been involved, the regulator added.

The competition commission, which began a preliminary investigation into currency trading in September, was among the first to probe manipulation in the $5.3 trillion-a-day currency market after Bloomberg News reported in June that traders colluded to rig the benchmark WM/Reuters rates. At least a dozen regulators around the world are now investigating.

“This is just another layer of a very large onion,” Christopher Wheeler, a London-based banking analyst at Mediobanca SpA, said by telephone. “The banks are trying really hard to cooperate with the regulators to minimize the financial impact, but the numerous investigations are going to drag on for at least two years.”

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